During a coelioscopic surgical operation, a patient's abdominal cavity is inflated by means of carbon dioxide. Incisions of small dimensions are formed on the abdominal wall and a trocar is introduced into each incision. The number of incisions depends on the type of envisaged operation and generally varies from 2 to 5. Each trocar corresponds to a hollow and tight tube into which a surgical tool is capable of sliding. An endoscope and surgical tools are introduced into the abdominal cavity via the trocar. The image supplied by the endoscope is captured by a camera and displayed on a display screen. During the surgical operation, an assistant displaces the endoscope according to the instructions given by the surgeon. By means of the video image supplied by the camera connected to the endoscope, the surgeon manipulates the surgical tools in the abdominal cavity according to the operation to be performed.
An advantage of a coelioscopic surgical operation is that it causes little trauma to the patient since the incisions made have small dimensions. However, the surgeon does not directly see the ends of the surgical tools located in the abdominal cavity and can only use the video image provided by the camera connected to the endoscope to perform the operation. A coelioscopic surgical operation thus requires for the surgeon to be highly experienced.
Positioning systems may be used instead of an assistant to displace the endoscope. It is for example the system commercialized by Computer Motion under trade name Aesop, the system commercialized by Armstrong Healthcare under trade name EndoAssist, or the system commercialized by Intuitive Surgical under trade name da Vinci Surgical System.
U.S. Pat. No. 8,391,571 describes a method of determining the position of a surgical tool in video images. The endoscope of the positioning system can then be automatically controlled from determined positions of the surgical tools and, for example, from an initial order issued by the surgeon.
A disadvantage of the method described in U.S. Pat. No. 8,391,571 is that it requires previously determining the position of the incision point of the surgical tool. This may in particular be achieved by a feeler having its position located by a tracking device or by triangulation from two images supplied by the endoscope. This previous step may be complex to implement.